Method for manufacturing steel sheets with layers of protective metal

ABSTRACT

In a method of manufacturing a steel sheet coated with a layer of protective metal wherein a powder of the metal is coated on the surface of the steel sheet and the coated steel sheet is dried and then rolled by means of a rolling mill to form a layer of the protective metal bonded to the surface of the steel sheet, a small quantity of atomized oil is electrostatically applied onto the surfaces of the rolls of the rolling mill and the applied oil is treated with equalizing rolls to form thin oil films of uniform thickness on the surfaces of the rolls whereby to prevent the powder of metal from adhering to the surfaces of the rolls.

United States Patent [1 1 Yamagishi et al.

[ Jan. 1,1974

[73] Assignee: Nippon Kokan Kabushiki Kaisha,

Tokyo, Japan [22] Filed: June 2, 1972 [21] Appl. No.: 259,287

[30] Foreign Application Priority Data June 16, 1971 Japan 46/42498 [52] US. Cl 29/420, 29/470, 72/236, 117/31, 228/4 [51] Int. Cl. B22f [58] Field of Search 29/420, 420.5, 470.9; 1 17/9, 22, 31; 148/627; 72/41, 43, 44, 45,

[56] References Cited UNITED STATES PATENTS 2,1xm4's 1/1940 Hudson ..ll7/3l 2,190,237 2/1940 Koehring 29/420 2,290,734 7/1942 Brassert 29/420 2,815,567 12/1957 Gould et al. 29/420 3,648,497 3/1972 Lang, Jr. et al 72/236 X 3,661,612 5/1972 Jackson et al. 117/31 X Primary Examiner-Robert D. Baldwin Assistant Examiner-Robert J. Craig Att0rney-Flynn & Frishauf [5 7] ABSTRACT In a method of manufacturing a steel sheet coated with a layer of protective metal wherein a powder of the metal is coated on the surface of the steel sheet and the coated steel sheet is dried and then rolled by means of a rolling mill to form a layer of the protective metal bonded to the surface of the steel sheet, a small quantity of atomized oil is electrostatically applied onto the surfaces of the rolls of the rolling mill and the applied oil is treated with equalizing rolls to form thin oil films of uniform thickness on the surfaces of the rolls whereby to prevent the powder of metal from adhering to the surfaces of the rolls.

4 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1 of the accompanying draw- This invention relatesto a method and. apparatus for ing, a steel sheet 1 coated with layers 2 of a powder of manufacturing a steel sheet coated. with a protective metal, aluminum for example, by applying, a powder of the metal upon the surface of the steel sheet and then rolling the coated steel sheet, and more particularly relates to a method of preventing the powder of the metal from adhering to the surface of rolls of the rolling mill.

Steel sheets are often'c'oated with a powder of aluminum and then the coated steel sheets continuously pass through a rolling mill. In such a case, the rolls of the mill should, desirably have clean and dry surfaces. However, the cleaner: the roll surfaces are, the more aluminum powder tends: to adhere. Although oil films formed on the surfaces of the rolls are effective to prevent the aluminum powder from' adhering to the roll surfaces, the coating of the aluminum powder before rolling is easily permeated. by oil, so that the quantity of the oil applied onto the roll surfaces should be small. If the quantity of the oil is excessive, for example more than 50 mg/m the aluminum powder tends to adhere to the rolls as if no oil film were formed thereon.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved method and apparatus for preventing the metal powder from adhering to the surfaces ofthe rolls of the rolling mill whereby to manufacture a steel sheet coated with a layer of protective metal firmly bonded thereto and having a beautiful finished surface.

According to one aspect of this invention there is provided a method of manufacturing a steel sheet coated with a layer of protective metalwherein a powder of the metal is coated on the surface of the steel sheet and the coated steel sheet is dried and then rolled by means of a rolling mill to form a layer of the metal bonded to the surface of the steel sheet, characterized in that a small quantity of' atomized oil is electrostatically applied onto the surfaces of the rolls of the rolling mill and the applied oil isleveled with equalizing rolls to form thin oil films of'uniform thickness on the surfaces of the rolls whereby to prevent the powder of the metal from adhering to the surfaces of the rolls.

According to another'aspect of the invention there is provided an apparatus for manufacturing a steel sheet coated with a layer of protective metal comprising a rolling mill including cooperating rolls between which a steel sheet coated with a powder of the protective metal is passed, means for electrostatically applying a small quantity of oil onto the surfaces of the rolls, and equalizing rolls cooperatingwith the rolls of the rolling mill for forming thin films of the oil on the surfaces of the rolls of the rolling mill.

BRIEF DESCRlPTlON OF THE DRAWING In the accompanying drawing:

FIG. I shows a diagrammatic side view of a rolling mill for coatings of the protective metal on the surfaces of a steel sheet;

FIG. 2 is a side view of an oiling device utilized in this invention;

FIG. 3 shows a perspective view ofa modified nozzle;

FIG. 4 is a cross-sectional view of the nozzle shown in FlG. 3 taken along a line lV-IV.

aluminum is rolled by passing it through the pair of rolls 3 of a rolling mill to form a steel sheet having uniform aluminum layers 7. When the surfaces of the rolls 3 are clean and dry, the powder of aluminum tends to adhere on the surfaces of the rolls. The powder of aluminum adhering on the rolls with small bonding force can be readily removed by means of a doctor knife 6, for example, but those firmly adhering can not be readily removed.

For this reason, it has been the practice to apply oil onto the surfaces of the rolls by means of oiling devices 5 and then forming uniform oil films by means of equalizing rolls 4. The quantity of the applied oil should be in a range of from 5 mg/m to 50 mg/m When the quantity of the oil is less than 5 mg/m aluminum powder tends to adhere to the surfaces of the rolls, whereas when the quantity of the oil exceeds 50 mg/m the oil permeates through the aluminum powder to reach the surface of steel sheet thereby decreasing the adhesiveness at the Al/Fe interface and causing the aluminum powder to adhere to the surfaces of the rolls.

The detail of the oiling device is shown in FIG. 2. Oil 9 in an atomizing tank 8 is atomized by the primary pressurized air 10 ejected from a nozzle 11 and the concentration of the atomized oil is adjusted by the secondary air admitted into the atomizing tank 8. The atomized oil is then ejected toward roll 3 through the slit 14 of a double walled nozzle 13. In front of the nozzle 13 is positioned an electrode 15 for ionizing the atomized oil ejected from slit 14. A source of high voltage power, not shown, is connected between the electrode 15 and roll 3 for causing the atomized oil to be charged at the electrode 15 and attached to the roll which is earthed to form a thin oil film on the surface of the roll.

FIGS. 3 and 4 show a modified nozzle 13 comprising concentric tubes 13a and 13b. The outer tube 13a has an elongated slit l4 and the inner tube 13b is connected with the atomizing chamber 8 through a pipe 16 and is provided with a slit 13c in parallel with a slit 14 but on the opposite side. The electrode may be provided in pipe 16 as at 15 as shown in FIG. 2.

The oil used may be a natural oil, such as cottonseed oil, or a synthetic oil such as dioctyl sebacate. However, mill oil of the aqueous emulsion type can also be used.

The equalizing rolls 4 may be made of felt, nonwoven synthetic fiber fabric or rubber. When made of metal, the doctor knife 6 not only removes the aluminum powder. adhered to the roll 3 but also serves as the grounding terminal of the roll. However, when the roll is grounded by another means, the doctor knife is not necessarily be made of metal.

The adjustment of the quantity of the applied oil can be accomplished by varying the flow of the secondary air while maintaining the pressure of the primary or atomizing air at a definite value. Since the adequate quantity of the secondary air varies dependent upon the type of the used oil, it is advantageous to plot calibration curves for respective oils.

EXAMPLE Oil films were formed under following conditions when aluminum layers having a thickness of 30 microns were formed by rolling on the surface of steel strips having a thickness of 0.8 mm.

Quantity Primary oisecond Electra Quantity air ary air, static of oil ressure Nmfl/ voltage applied Example g./cm. Oil min V Material oi equalizing r011 mg./m

1.0 Dioetyl sebacate... 5 3.0 o 50 0.7 Cottonseed oil. 1.5 ...do 50 0. 7 30% aqueous emulsion of oil 20 1.0 .....do 50 Trademark In examples I3 and 5 no aluminum powder adhered to the surfaces of the rolls and it was possible to continuously manufacture aluminized steel sheets having beautiful surface finish without the necessity of using the doctor knife.

in the cases of examples 2, 4 and 6, however, since the quantity of the applied oil have exceeded the upper limit, aluminum powder often adhered to the surfaces of the rolls. However, it was possible to readily remove the powder with the doctor knife because the powder is adhering with a small bonding force, thus causing no trouble for the continuous production.

According to this invention, since the rolling oil is electrostatically applied to the rollers, it is possible to improve the efficiency of utilization of the oil and to minimize the quantity of the applied oil so that post treatment of degreasing is not necessary. Moreover, as the quantity of the applied oil is small, adhesion of the metal powder to the roll surface can be effectively prevented, thus assuring continuous rolling of metal coated steel plates having a beautiful surface finish.

While the invention has been shown and described in terms of specific embodiments, it will be clear that many changes and modifications may be made without departing from the scope of the invention. For examomize the oil and then convey the atomized oil by the same electrostatic field as is well known in the art of electrostatic coating.

What is claimed is:

1. In a method of manufacturing a steel sheet coated with a layer of protective metal wherein a powder of the metal is coated on the surface of the steel sheet and the coated steel sheet is dried and then rolled by means of a rolling mill to form a layer of the metal bonded to the surface of the steel sheet, the improvement which comprises the steps of electrostatically applying a small quantity of atomized oil onto the surfaces of the rolls of said rolling mill and leveling the applied oil with equalizing rolls to form thin oil films of uniform thickness on the surfaces of said rolls whereby to prevent said powder of the metal from adhering to the surfaces of said rolls.

2. The method according to claim 1 wherein said metal is aluminum.

3. The method according to claim 1 wherein the quantity per unit area of said oil applied onto the surfaces of said rolls ranges from 5 to 50 mg/m*.

4. The method according to claim 1 wherein said oil is selected from the group consisting of natural oils,

synthetic oils and an aqueous emulsion of oil. 

2. The method according to claim 1 wherein said metal is aluminum.
 3. The method according to claim 1 wherein the quantity per unit area of said oil applied onto the surfaces of said rolls ranges from 5 to 50 mg/m2.
 4. The method according to claim 1 wherein said oil is selected from the group consisting of natural oils, synthetic oils and an aqueous emulsion of oil. 